1. Field of the Invention
The present invention relates to a lens barrel provided with a mechanism to move the lens in the directions of an optical axis, and an optical instrument having the lens barrel thereof.
2. Description of Related Art
As a conventional mechanism for adjusting respective gaps between a plurality of lenses for zooming or focusing in a lens barrel in optical instruments such as cameras or the like, generally there are such ones that make a fine adjustment by inserting a spacer in a lens frame, or that move a lens frame in the directions of an optical axis by use of a helicoidal screw.
However, there are such problems that, in the case of the former, a number of steps are required for removing and reattaching a lens frame in order to select and provide an optimal adjustment spacer, and also, in the latter case, a backlash of the helicoidal screw may affect various functions of the optical instrument.
In the meantime, there has been proposed a method for adjusting the position of a lens in the directions of an optical axis, comprising the steps of forming a reference plane in a hold frame for supporting a lens frame in a stepwise manner, and rotating the lens frame around its own axis so as to alter the reference plane to adopt as disclosed, for example, in the following.
Japanese Patent Application Publication No. 2002-350702.
According to this technique described above, an optimum state of optical adjustment is achieved by abutting a protrusion provided on a rear side of the lens frame against either one of stepwise stages on the holding frame for holding the lens frame. After the optical adjustment having been completed, the lens frame is secured to the holding frame thereof by bonding or the like.
The aforementioned related art, however, is associated with such a problem that because its lens cannot be secured to any one of the reference planes selected during the optical adjustment, the lens is set afloat during the adjustment. Although it may be considered independently to provide an additional mechanism to press the lens frame against the reference plane, there may result in such drawbacks as of an increased number of parts, an increased cost of manufacture, and an increased space for installation thereof.